Many metalworking shops specialize in precision metal cutting and grinding, especially for multiples of the same workpiece. The machine tools required for such work are very expensive. Economic use of these tools is accomplished by maximum run time and minimum downtime for workpiece setup. One method of achieving minimum downtime is to use setup fixtures dedicated to each different batch of workpieces. For example, a milling machine vise may be modified to support each part, in a batch of workpieces, in a particular position for milling a slot and boring a hole. As long as the vise is not moved relative to the tool, each workpiece can be machined exactly the same by repeating the tool path for each setup. In this manner setup time is minimized, even though precision milling vises are expensive to dedicate to particular workpieces.
A number of different workpiece positioning devices have been invented to locate workpieces in a milling machine vise. Examples are illustrated in U.S. Pat. No. 4,598,480 to Cukelj, U.S. Pat. No. 4,030,718 to Philipoff, U.S. Pat. No. 4,020,742 to Raymond, and U.S. Pat. No. 3,810,311 to Pingel. They are characterized by posts or blocks holding contact arms which enter the opening between vise jaws to contact a workpiece, thereby preventing its lateral movement until the vise jaws can be closed on the workpiece. The posts and blocks are connected either to the milling machine table by T-slot brackets or to the vise by threaded connection. Most are deficient in that the interruption of a batch milling job, wherein the device is moved, necessitates readjustment of the device after it is reinstalled to continue running the batch of parts. Unlike a dedicated vise, most of these positioning devices are not designed to be removed and reused with a particular batch of workpieces with minimum setup time.
The device of Raymond provides for contact arm removal and replacement without adjustment. However, it is quite complex in terms of its large number of precision parts. Its cost may approximate that of a dedicated vise.
Another deficiency of most prior art positioning devices is their workpiece contact surfaces are not maintained square to the vise jaws throughout their ranges of adjustment. Squareness is particularly desired for curved workpiece surfaces such as vertical axis cylinders and horizontal axis disks. Without such squareness the positioning device must contact the exact center of the workpiece to repeatedly position it accurately. Contacting the exact center of a curve is a difficult setup.
A disadvantage of vise-mounted prior art positioning devices is their need for modification of a precision vise in order to attach the device. Typically, holes are drilled and tapped into the top or side surfaces of a vise so that an attachment screw may be threaded into the vise to secure the positioning device to the vise.